Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$21.37	6.491%	$22.7571	$22.76	$22.75	$22.80
Purchase #2	$89.90	11.115%	$99.8924	$99.89	$99.90	$99.90
Purchase #3	$43.64	5.316%	$45.9599	$45.96	$45.95	$46.00
Purchase #4	$21.83	3.803%	$22.6602	$22.66	$22.65	$22.70
Purchase #5	$12.81	10.813%	$14.1951	$14.20	$14.20	$14.20
Purchase #6	$116.75	11.458%	$130.1272	$130.13	$130.15	$130.10
Purchase #7	$73.97	11.221%	$82.2702	$82.27	$82.25	$82.30
7 purchase totals =	$380.27		$417.8621	$417.87	$417.85	$418.00